Fix compilation warning.
Fix compilation warning.

* test/test_context.c
  (): Include "serf_private.h" for serf_log().

TommyU/serf,wzugang/serf,krime/serf,krime/serf,krime/serf,TommyU/serf,blueszhangsh/serf,wzugang/serf,Manouchehri/serf,liuzongquan/serf,sworda/serf,blueszhangsh/serf,sworda/serf,justinweb/serf,sworda/serf,idomon/serf,Manouchehri/serf,muthusuba/serf,wzugang/serf,blueszhangsh/serf,idomon/serf,sworda/serf,muthusuba/serf,Manouchehri/serf,liuzongquan/serf,muthusuba/serf,idomon/serf,TommyU/serf,blueszhangsh/serf,justinweb/serf,TommyU/serf,Manouchehri/serf,idomon/serf,justinweb/serf,justinweb/serf,liuzongquan/serf,liuzongquan/serf,wzugang/serf,krime/serf,muthusuba/serf